This application claims the priority of German Patent Document 199 49 666.8 filed Oct. 14, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an arrangement for condensing a fiber strand leaving a drafting unit, which fiber strand passes through a condensing zone in a twist-free state and is transported in the condensing zone, deposited on an air-permeable, moving transport element, over a stationary suction slit arranged diagonally to the direction of motion of the transport element, said suction slit defining the direction of a suction air stream by a guiding edge, which air stream positions the fibers of the fiber strand diagonally to the direction of motion of the transport element and so condenses the fiber strand.
An arrangement of this type is prior art in the technical magazine Spinnovation No. 5/99 from the Spindelfabrik Suessen, a German company. A woven fabric belt in the form of a narrow perforated transport belt serves here as a transport element, to whose direction of motion the suction slit extends slightly diagonally. The effective width of the suction slit is significantly larger than the width of the fiber strand in condensed state, and is constant for the whole width.
It is important for the pneumatic condensing of a fiber strand leaving a drafting unit that the fiber strand is transported in the condensing zone deposited on an air permeable transporting element in an untwisted state and having fibers lying essentially parallel to one another, and that in the condensing zone an air stream is generated which passes through the transport element, the width and/or direction of said air stream determining the degree of condensing, and positioning the fibers diagonally to the transport direction and thus bundling or condensing the fiber strand.
In practice it has been established that during pneumatic condensing a certain amount of fiber fly occurs and that in addition single fibers, in particular edge fibers of the fiber strand to be condensed, can wind themselves around a roller of the front roller pair when leaving the drafting unit.
It is an object of the present invention to ensure that as many fibers as possible of the fiber strand to be condensed are bundled in the condensing zone without any significant fiber fly occurring.
This object has been achieved in accordance with the present invention in that the suction slit begins with a starting width which encompasses the not yet condensed fiber strand on its entire width, and directly downstream thereof graduates, in the form of a delta, into a narrower effective width of the diagonal suction slit, whose guiding edge continues an edge of the delta without deformation.
It has been shown that in the case of an embodiment of the suction slit of this kind, all fibers, including the edge fibers of the delivered and to be condensed fiber strand are reliably seized, so that undesirable circulating fibers are avoided on the front roller pair of the drafting unit, and that practically no fiber fly arises which could escape from the condensing zone. This applies in particular when a certain amount of drafting tension of approximately 6% to 10% is to be produced during the condensing of the fiber strand.
The slight diagonal of the guiding edge serves the purpose of not only laterally bundling the fibers of the fiber strand to be condensed, but also, in connection with the direction of motion of the transport element, to impart a light false twist, which increases the bundling effect.
It is already known in German published patent application 44 26 278 to permit a suction slit of a condensing zone to begin with a relatively large initial width and then to permit the suction slit to taper delta-like and to continue with a narrower end width. At least half the entire length of this known suction slit, which is not arranged diagonally to the direction of motion of the transporting element, is taken up by the delta form. This measure serves a completely different purpose to the one in the present invention. The relatively long delta permits namely with its diagonal edges a traversing of the delivered fiber strand, whereby the edges of the suction slit are not arranged parallel to one another, but rather completely symmetrically triangle-like. The fiber strand is disposed alternatively during transversing on the right and on the left edge of the delta and subsequently transferred over to the end area of the slit which extends in a straight line to the transport element. In contrast, in the case of the present invention, the fiber strand to be condensed is disposed on the same edge throughout, namely on a guiding edge which extends diagonally to the direction of motion of the transport element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.